This guide will walk you through the process of modifying an ELM327 OBD2 scanner to interface directly with an Arduino microcontroller. This “Hacked Obd2” approach allows for custom automotive diagnostics, data logging, and control applications by leveraging the ELM327’s OBD2 communication capabilities and the Arduino’s processing power and flexibility.
Disassembling the ELM327 Scanner
The first step in this modification is to carefully disassemble your ELM327 OBD2 scanner. Most ELM327 scanners come in a plastic enclosure that is typically held together by screws.
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Remove the Sticker: Begin by peeling off any sticker that might be covering the screw holes on the ELM327 enclosure. This will expose the screws needed to open the device.
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Unscrew the Enclosure: Using a small star screwdriver (also known as a Torx screwdriver), carefully remove the four screws located on the corners of the enclosure. Keep these screws in a safe place as you will need them for reassembly.
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Open the Casing: Once the screws are removed, gently separate the two halves of the ELM327 enclosure. Inside, you will find the circuit board containing the ELM327 chip and other components.
Tip for Connector Orientation: Before proceeding further, if you plan to remove the connector that links the circuit board to the OBD2 port, it’s a good idea to mark one side of the connector with nail polish or a marker. This simple step will help you remember the correct orientation when reconnecting it later. However, for this specific “hacked OBD2” modification, it’s not strictly necessary to remove this connector.
Identifying and Accessing TX and RX Pins
To communicate with the ELM327 chip using an Arduino, you need to connect to its serial communication pins, specifically the Transmit (TX) and Receive (RX) pins.
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Locate TX and RX Pins: Refer to the pin-out diagram of the USB bridge chip on your ELM327 board. This diagram will indicate the location of the TX and RX pins. In many common ELM327 boards, these pins are clearly labeled or can be identified based on the USB bridge chip datasheet. The image below illustrates typical TX and RX pin locations.
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Solder Wires to TX and RX: Carefully solder two wires to the TX and RX pins on the ELM327 board. Use thin gauge wires to minimize stress on the small solder pads. Exercise caution during soldering to avoid accidentally desoldering any nearby surface-mounted components. If you are new to soldering, practice on scrap electronics first to get comfortable with the process.
Tip for Pin Identification: If you are unsure which pins are TX and RX, you can use a simple method with your Arduino. Program your Arduino to continuously send data to the serial monitor with short delays. Connect a jumper wire to the Arduino’s TX pin and gently probe around the pins on the ELM327 board. Observe the surface-mounted LEDs on the ELM327 board. When you touch the correct RX pin, the LEDs should flicker, indicating serial communication activity. While this method primarily helps identify the RX pin (of the ELM327, to connect to Arduino TX), the TX pin (of the ELM327, to connect to Arduino RX) is usually adjacent or clearly indicated in the chip’s pinout diagram, often found online by searching the chip number. The provided images also clearly show the typical locations of these pins.
Modifying the USB Connection for Arduino Control
To ensure that the Arduino has exclusive control over the ELM327’s serial communication and to prevent interference from a connected PC, it’s advisable to modify the USB connection.
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Isolate Data Pins: The USB cable connecting to the ELM327 board typically has four pins: power (VCC), data positive (D+), data negative (D-), and ground (GND). To isolate the ELM327 for Arduino control, you should cut or disconnect the data positive (D+) and data negative (D-) pins. Crucially, only cut the middle two pins, leaving the power and ground pins intact. This allows the ELM327 to still receive power from the USB port while preventing data communication with a computer.
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Maintain Power Supply: By only cutting the data pins, the ELM327 will still receive power from the USB port when connected to your computer or a USB power source. This is essential for it to operate and communicate with the Arduino via the soldered TX and RX wires.
NOTE: This USB modification is crucial for dedicated Arduino control. By preventing the ELM327 from establishing a USB data connection, you ensure that the serial interface is exclusively available for communication with your Arduino, enabling seamless “hacked OBD2” functionality.
Reassembly and Implementation
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Reassemble the Enclosure (Optional): After completing the modifications, you can reassemble the ELM327 enclosure using the screws you removed earlier. However, in some automotive setups, especially for prototyping or in-car installations where space is limited, you might choose to leave the enclosure off. The original author mentions taping it up due to space constraints in their Jeep.
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Connect to Arduino: Connect the wires you soldered to the ELM327’s TX and RX pins to the corresponding RX and TX pins on your Arduino board, respectively. Ensure you connect TX to RX and RX to TX for proper serial communication.
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Program Your Arduino: You can now program your Arduino to communicate with the “hacked OBD2” ELM327 scanner. Use Arduino libraries designed for OBD2 communication or implement the ELM327 command set directly in your code to send commands and receive data from your vehicle’s OBD2 port.
By following these steps, you’ve successfully created a “hacked OBD2” interface, allowing you to use an ELM327 scanner with an Arduino for custom automotive projects. Remember to always exercise caution when working with electronics and vehicle systems. Further research into OBD2 protocols and ELM327 command sets will enhance your ability to create powerful and customized automotive applications.
